Edit > Undo reverses the last change made to the story.
Edit > Redo restores the last change undone. When you make a new change, Redo is no longer available.
Undo and Redo are currently available for:
When you make a change that is not yet undo-able, Undo is no longer available. That is, you can only undo the most recent changes that are undo-able.
Saving the information required to undo all your changes requires memory. If Springboard uses up too much memory on undo information, you may want to Clear Undo Information.
The shortcut key for Undo is Ctrl+Z. The shortcuts for Redo are Ctrl+Shift+Z and Ctrl+Y.